What is Aluminum Anodizing and How Does It Work

To maximize the durability and performance of aluminum parts, many companies source aluminum anodizing services to both enhance the surface finish and add an effective layer of protection to their workpiece. Anodizing aluminum is a popular, efficient coating method, that is often more cost-effective and durable than many traditional surface applications, like painting. Using a controlled electrochemical process, aluminum anodizing creates an exceptionally hard, durable, corrosion-resistant, and non-conductive anodic oxide finish on aluminum parts. Along with durability, this anodized layer results in a smooth, attractive surface that can be dyed in many colors.

Also referred to as an “aluminum oxide finish”, anodic oxide finishes are electrochemically fused to the surface, leaving a permanent protective layer that will never peel or chip like paint or even powder-coated surfaces. This is because the electrochemical fusion process allows the new anodic oxide layer to become physically bonded to the aluminum workpiece. Additionally, the surface finish on anodized aluminum products can enhance the adhesion of secondary coatings like paint.

Relative to other available aluminum finishes, anodizing is very environmentally friendly.  Most chemicals used in the process are non-hazardous and are often used in fertilizers and water purification facilities.  Very, very small amounts of nickel and trivalent chromium are used in the seal and dye processes.  These are separated from the waste stream and handled by certified waste handling operations.

The anodizing process can be divided into three general categories: Surface preparation, anodizing, and finishing.

In surface preparation, the parts may be tumbled or bead blasted.  They are thoroughly cleaned in a non-etching caustic detergent.  They may then be etched to make the surface more matte and offset the anodizing growth to maintain dimensions.  It is then important that alloy metals and native oxide on the surface are removed.

During the anodizing process, the aluminum is submerged in a bath of acid electrolytes. Once submerged, the aluminum workpiece acts as an anode, with a cathode being placed beside it.  Electric current is forced through the bath, resulting in the bath solution releasing oxygen ions that will react with the aluminum workpiece forming an anodized surface finish.

The anodized surface may then be dyed.  There are about 40 billion pin holes in the sapphire-like aluminum oxide layer.  Microdroplets of pigment are adsorbed into these pin holes.  The pigments can be seen through the transparent aluminum oxide, changing the apparent color of the part.  The part is then sealed.  This process is done to trap the pigments in the pinholes and to protect the exposed aluminum in the bottom of the pinholes from environmental conditions.

Whether you need a single part finished, or an entire production line – we have the experience, in-house capabilities, and dedicated staff to make it happen. We also offer custom aluminum anodizing services, aluminum chem film services, and aluminum chromate conversion coating services. For more information on any aspect of our business, call Sapphire Metal Finishing at 208-614-4050, visit our contact page, or use our quote generator tool for quick price estimates.

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